Germanium Deposition on Silicon: Surface Chemistry of (CH 3 CH 2 ) 2 GeH 2 and GeC1 4
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GERMANIUM DEPOSITION ON SILICON: SURFACE CHEMISTRY OF (CH3CH2)2GeH2 AND GeC14 P.A. Coon, M.L. Wise, A.C. Dillon and S.M. George Dept. of Chem. and Biochem., Univ. of Colorado Boulder, Colorado 80309 ABSTRACT Diethylgermane, (CH3CH2)2GeH2, and germanium tetrachloride, GeCI4, may be useful precursors for chemical vapor deposition (CVD) or atomic layer controlled deposition of germanium. To explore the surface chemistry of these alternative precursors, the adsorption and desorption kinetics of (CH3CH2)2GeH2 (DEG) and GeCl4 on Si( 111) 7x7 have been examined using laser-induced thermal desorption (LITD), and temperature programmed desorption (TPD) techniques. Fourier transform infrared (FTIR) spectroscopy has also been employed to monitor the decomposition of DEG on porous silicon surfaces. The FTIR spectra revealed that DEG dissociatively adsorbs on porous silicon surfaces at 200 K to form Sill, GeH, and SiCH2CH3 surface species. No spectral features were observed for GeCH2CH3 surface species. The TPD studies following DEG exposures on Si(111) 7x7 observed CH2=CH2 and H2 desorption products at 700 and 800 K, respectively. The production of CH2=CH2 (ethylene) was consistent with a 19-hydride elimination mechanism from surface ethyl species, i.e. SiCH2CH3(ad) --> SiH(ad) + CH2=CH2 (g). Similar TPD experiments following GeCI4 exposures monitored the desorption of only SiCl2 at approximately 920 K. Desorption of SiC12 indicates that the chlorine on GeC14 has transferred to the silicon surface. Atomic Ge was also observed to desorb at 1200 K following both DEG and GeCl4 adsorption. LITD experiments measured initial reactive sticking coefficients of So -0.05 for DEG and So -1.0 for GeC14 at 200 K. As expected from a precursor-mediated adsorption model, the sticking coefficients decreased versus increasing surface temperature. The sticking coefficients for these germanium containing precursors were higher than the corresponding sticking coefficients for (CH3CH2)2SiH2 and SiCl4. Possible recipes for the CVD or atomic layer controlled deposition of germanium on silicon can be proposed based on the surface chemistry and adsorption and desorption kinetics for DEG and GeCI4. INTRODUCTION Germanium deposition on silicon surfaces is important because of the possibility of bandgap manipulation in devices with Si/Si1_xGex/Si heterostructures (1). CVD growth of Sii1xGex alloys has been accomplished using GeH4 and Sill4 or SiHI2CI2 (2,3). Diethylgermane (DEG), (CH3CH2)2GelH2 and germanium tetrachloride, GeCI4, are possible molecular precursors for germanium atomic layer controlled growth (4,5). However, the surface chemistry of these alternative germanium molecular precursors has not been studied, and the possibility of atomic layer controlled deposition has not been developed. In this study, laser-induced thermal desorption ([ITD), temperature programmed desorption (TPD), and Fourier transform infrared (FTIR) spectroscopic techniques were used to investigate the reaction products and kinetics following DEG and GeCC4 reaction on silico
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